In GERAN systems, the Mobile Stations, the MSs, receive bursts transmitted from a BTS, a Base Transceiver Station. A burst comprises information such as data and uplink status flags, USFs, for the MS, and also comprises a Training Sequence Code, a TSC. The BTS can modulate each burst in a number of different ways, i.e. using one of a number of different modulations, and for each modulation type, there exists one set of TSCs. At present, these sets of TSCs comprise 8 TSCs per set.
Each MS is assigned a TSC, which is used by the MS for burst time synchronization, and also in order to estimate the radio channel and to perform blind modulation detection, i.e. to blindly detect the modulation that is used for transmitting the received burst. If the TSC comprised in the burst corresponds to the TSC assigned to the MS, these three operations (synchronization, channel estimation and blind modulation detection) can be performed successfully, and the MS thereby knows that the information comprised in the burst may be for the MS. Whether or not the information comprised in the burst is in fact for the MS is then determined by the MS by examining the information comprised in the burst.
The TSCs are a sequence of, at present, 26 or 31 bits, which is placed as a so called midamble in a burst.
The bursts in the downlink are transmitted to the MS from the BTS, but the information for the MS comes from a Base Station Controller, a BSC, which controls the BTS and uses the BTS to communicate with the MS. The bursts are received by the MS on a Temporary Block Flow, a TBF, between the MS and the BSC, where the TBF goes via the BTS.